How Peristaltic Pumps Work
Rotary motion is
transferred into a linear motion via rotating rollers or “shoes” against an
elastomeric hose, pinching it sufficiently to move the contents of the hose
in the direction of rotation.
The flow rate is
somewhat proportional to the rotational speed with a key variable being the
amount of hose compression. While laboratory size peristaltic pumps
utilize non-reinforced tubing and completely “pinch” the tube to provide
accurate dosing, industrial size peristaltic pumps are not typically
operated in that fashion because the hoses are more rigid and would require
replacement frequently if they were compressed completely.
industrial peristaltic pump always has some “slip”, especially if the
discharge pressure is higher and the fluid has a water-like viscosity.
Thus higher viscosity fluids can be pumped at higher pressures than lower
viscosity fluids when the hose isn’t pinched closed 100%.
Peristaltic Pump Hose Design
Hoses used for
industrial peristaltic pumps are designed specifically for repeated
compression and are not to be confused with “standard hoses”. Some
hoses consist of homogeneous extruded materials and others consist of
several layers having reinforced fiber rings within those layers to provide
increased rigidity to maintain the circular cross section when not
peristaltic pump hose needs replacement when the dosed volume decreases to
an unacceptable level, which is a reflection of the hose remaining somewhat
elliptical shaped even when not being compressed. This “hose fatigue”
can eventually result in cracking or delamination of the internal layer if
it is a lined hose design. It is preferable to replace a hose before
it completely fails, to prevent the process fluid from leaking into and
potentially out of the pump.
t is a little known
“industry secret” that most peristaltic pump manufacturers use the same few
hose manufacturers and this is because the hose design is especially
complex. The hoses we provide for our Vector series of peristaltic
pumps will also work in Verderflex®
and Watson-Marlow Bredel™
to our cross-reference chart with pricing).
Roller and Shoe Design
We offer both roller
and shoe designs for hose compression. A roller design is slightly
more gentle to the hose during compression as the rollers roll against the
surface as the hose is compressed. A shoe design is simultaneously
compressing and rubbing against the hose surface and therefore usually a
lubricant is used with shoe designs to help extend hose life. The shoe
design and addition of a lubricant to be contained within the pump body
increases the complexity and cost for shoe style peristaltic pumps.
Shoe designs are
capable of higher pressures and therefore the decision for which design is
best for a given application is usually both pressure and application based.
Roller designs only
require a light coating of silicon grease on the hose surface because the
roller “rolls” across the hose surface. Therefore applications
involving food and beverages might benefit from this design as the potential
for cross contamination if a hose fails is less than shoe design pumps
bathed in a lubrication oil – even if that oil is “food grade”, it is still
often preferable to go with a roller design.
the pressures are not high, the roller design should provide longer hose
life and overall be a more cost effective solution.
Advantages of Peristaltic Pumps
The most recognizable
advantage peristaltic pumps provide compared to other types of positive
displacement pumps is that the hose is the only component exposed to the
pumped fluid. It is therefore lacking mechanical seals and packing, aspects
prone to wear and leakage for other pump designs.
also do not have internal check valves to control the direction of flow and
therefore can handle relatively large solids and fibrous (long) solids,
which would cause havoc in pumps such as air operated diaphragm pumps that
utilize ball-check valves to control the flow direction.
Since there are no
moving, sliding or rotating components dependent upon the fluid being pumped
for lubrication or cooling, peristaltic pumps can operate dry and are often
used to “suck dry” tanks and totes.
hoses can be replaced with minimal effort – the design of a peristaltic pump
is rather simplistic from a user’s perspective, so it is easy to replace a
hose and to know when a hose requires replacement. There are no other
parts to replace!
Proper Sizing of Peristaltic Pumps
The hose size (it’s
ID), the amount of compression and the frequency of compression will dictate
the flow rate. Our sizing guidelines are to operate the pump near 30
RPM (the slower the better) and the resulting hose life should be 1,500 to
2,000 hours for fiber-braided hoses. (extruded hoses 700 to 1,000 hours).
Since hose life is directly proportional to the amount and frequency of
compression, utilizing a larger size peristaltic pump will enable you to
operate at lower RPM’s and requires less hose compression. The initial
cost difference between two different size pumps might be quickly
offset by longer hose life and less frequent hose
replacements. If your pump will operate for >8 hours daily you should
select a pump which operates close to 30 RPM. Likewise, if your pump
is used for only a few hours daily/weekly, you can operate it at 60-90 RPM.
The pump shaft speed
is achieved via a gearbox or gear-motor, because using a mechanical speed
reduction with a standard 1800 RPM motor reduces the motor size (HP)
required. Once a gearbox/motor is selected, the maximum shaft speed is
fixed and you can use an optional VFD to further reduce the shaft speed if
The amount of
compression applied to the peristaltic hose is adjustable by installing
shims under the roller or shoe mounts. The initial set-up procedure
involves installing shims until the desired flow is achieved, thus
compressing the hose minimally.
If you have
peristaltic pumps, talk to us about your application and pump model and we
will help ensure you are using the best hose design and at a competitive
If you are using an
air operated diaphragm pump and experience frequent check valve fouling or
wish to reduce your compressed air consumption, contact us and we will
review your application to see if a peristaltic pump would be a good
alternative.Our goal is to help
you solve your application in the most cost effective and reliable manner
possible, let our 25+ years of experience go to work for you today!